1. Field of the Invention
The present invention relates to an ink ribbon cassette and a thermal transfer printer using the same, and more specifically, to an ink ribbon cassette being capable of feeding and discharging recording papers printed over the entire page properly, and a thermal transfer printer using the same.
2. Description of the Related Art
As shown in FIG. 11, a thermal transfer printer 100 in the related art includes a hollow box-shaped frame 101.
The frame 101 includes a side plate member 101a provided on the near side, a side plate member 101b provided on the far side opposed to the side plate member 101a, a top plate 101c provided on top, and a bottom plate 101d provided at the bottom.
A cassette mounting portion 102 for mounting an ink ribbon cassette 110 that will be described later is arranged in the hollow portion of the frame 101, and a cassette insertion slot 102a is formed on the side plate member 101a so as to continue into the cassette mounting portion 102.
Disposed between the side plate members 101a, 101b of the frame 101 is a rotatable platen roller 104.
At the position opposed to the platen roller 104, there is provided a thermal head 106, which is attached on the head mounting base 107.
The head mounting base 107 is formed into substantially rectangular shape in plan view, and mounted on one of the side plate member 101b in a cantilevered manner.
A wall member 113 is disposed in the frame 101 on the left end side, and the wall member 113 is formed with a paper feeding and discharging port 110a in communication with the cassette mounting portion 102.
The frame 101 is provided with a paper feed roller 111 in the vicinity of the platen roller 104, and a pressure contact roller 112 being capable of establishing pressure contact with the paper feed roller 111, and being capable of rotating with the paper feed roller 111, so as to be pressure contact therewith.
As shown in FIG. 12 and FIG. 13, the ink ribbon cassette 110 to be attached on and detached from the thermal transfer printer 100 in the related art integrates a cassette body 115 having a substantially elliptical hollow portion for storing an ink ribbon 114, and a ribbon guide member 118 extending from the cassette body 115 on one side.
The cassette body 115 includes a feed core 116 and winding core 117 on which both ends of the ink ribbon 114 are wound stored therein.
As shown in FIG. 12, the cassette body 115 is formed with a slit-shaped ribbon outlet port 115c for allowing the ink ribbon 114 wound on the feed core 116 to be drawn out from the cassette body 115.
A triangular paper guide member 115e is disposed in the vicinity of the ribbon outlet port 115c so as to project from the cassette body 115 in the direction in which the ink ribbon 114 is drawn.
The paper guide members 115e are respectively formed at the positions near the widthwise ends of the ink ribbon 114 drawn out from the ribbon outlet port 115c. 
As shown in FIG. 14, a ribbon sliding wall 118a connecting a pair of sidewalls 115a of the cassette body 115 are formed under the ribbon guide member 118.
The upper portion of the ribbon sliding wall 118a is formed with a ribbon running groove 118b of a prescribed clearance.
The ribbon guide member 118 is formed with a ribbon turning-back portion 118c at the right end in FIG. 12, and a rotatable roller is disposed at this ribbon turning-back portion 118c. 
A head mounting base 107 cantilevered by the side plate member 101b of the frame 101 may be inserted between the ink ribbon 114 drawn out from the ribbon outlet port 115c and the ribbon sliding wall 118a. 
As shown in FIG. 14, when the ink ribbon cassette 110 is mounted on the cassette mounting portion 102, a clearance 120 is defined between a bottom surface 115d of the cassette body 115 and the bottom plate 110d of the frame 101, and the clearance 120 continues to the paper feeding and discharging port 110a, so that the recording paper 20 to be fed or discharged by the paper feed roller 111 may be carried through the clearance 120 laterally of FIG. 14.
As shown in FIG. 12, the ink ribbon 114 may be drawn out once through the ribbon outlet port 115c by the rotation of the winding core 117 in the direction indicated by the arrow E in FIG. 12, passed through under a head insertion portion in the direction indicated by the arrow G, and turned back at the ribbon turning-back portion 118c. From this state, the ink ribbon 114 may be traveled over the ribbon sliding wall 118a of the ribbon guide member 118, drawn into the cassette body 115 again from the ribbon running groove 118b, and then wound on the winding core 117.
As shown in FIG. 16, the recording paper 20 is generally formed of a cut sheet of prescribed dimensions having a leading edge 20a and a trailing edge 20b, and is formed with a printing area (print-recording surface) 20c at the central wide range, and non-printing areas 20d, 20d at the positions out of the printing area 20c near the widthwise ends thereof. The boundary between the leading edge 20a and the printing area 20c agree with a print starting position 20s on the recording paper 20.
When an image is recorded on the recording paper 20 by the thermal transfer printer 100, a desired image is recorded within the printing area 20c. When printing the image by full-page printing mode (rimless printing mode) on the recording paper 20, the non-printing areas 20d, 20d are also included within the printing area.
Referring now to FIG. 14 through FIG. 16, the print-recording operation by the ink ribbon cassette 110 mounted on the thermal transfer printer 100 in the related art will be described.
When the ink ribbon cassette 110 is mounted on the cassette mounting portion 102, the ink ribbon 114 drawn out from the ribbon outlet port 115c takes the position between the thermal head 106 and the platen roller 104.
The recording paper 20 inserted from the paper feeding and discharging port 110a is carried toward the ribbon turning-back portion 118c, and then the platen roller 104 raised toward the thermal head 106 resiliently compresses the thermal head 106 together with the ink ribbon 114. Then a plurality of heating elements selectively heated on the thermal head 106 transfer melted ink on the recording paper 20 to perform a desired printing.
When the desired printing is terminated, the platen roller 104 is lowered to move away from the thermal head 106, and the recording paper 20 is carried outward by the rotation of the paper feed roller 111 and the pressure contact roller 112.
Subsequently, when printing a color image on the recording paper 20, the ink ribbon cassette 110 containing an ink ribbon 114 on which different colors of ink, such as magenta, cyan, yellow, and so on are formed in sequence is used. Then the platen roller 104 is moved up and down repeatedly, and the paper feed roller 111 is repeatedly rotated forwardly and inversely (reversely) for allowing reciprocating motion of the recording paper 20, so that the colors such as magenta, cyan, and yellow are printed superimposingly in sequence at a prescribed position on the recording paper 20 to print a desired color image.
Therefore, the recording paper 20 printed with ink in one color is positioned in such a manner that the trailing edge 20b of the recording paper 20 is located between the paper feed roller 111 and the pressure contact roller 112. In this state, the paper feed roller 111 stops rotation (forward rotation) once, then, in order to carry the recording paper 20 in the reverse direction (the direction indicated by the arrow k in FIG. 14), the direction of rotation of the paper feed roller 111 is inversed (reversed) to allow the print starting position 20s of the recording paper 20 to locate between the thermal head 106 and the platen roller 104 again. Subsequently, the printing operation as described above is repeated to print with ink of other different colors.
Such thermal transfer printer 100 in the related art is adapted in such a manner that the recording paper 20 can be carried in a state in which the recording paper 20 is kept in sliding contact with the upper surface of the paper guide member 115e of the ink ribbon cassette 110 even when the recording paper 20 is carried repeatedly in the directions indicated by the arrows j, k during color printing.
[Problems to be Solved by the Invention]
However, as shown in FIG. 15, when the recording paper 20 printed on its printing surface 20c is inversely carried in the direction indicated by the arrow k in FIG. 14, the printing surface 20c of the recording paper 20 comes into sliding contact with the upper surface of the paper guide member 115e of the cassette body 115. Therefore, in the case where the recording paper 20 is fed in a state of being displaced in the lateral direction, a part of the printing surface 20c is rubbed and thus the printing quality may be deteriorated.
In addition, there is such problem that the quality of the image recording is significantly deteriorated when printing over the entire page of the recording paper 20 according to the needs of the user of recent years, because the printing surface 20c of the recording paper 20 comes into direct contact with, and thus is rubbed by, the upper surface of the paper guide member 115e. 
The invention intends to provide an ink ribbon cassette being capable of feeding and discharging printed recording paper properly without causing deterioration of the quality and a thermal transfer printer using the same.
As a first measure for solving at least one of the problems described above, there is provided an ink ribbon cassette including: a hollow cassette body having a top plate and a bottom plate so as to face toward each other and a wall plate disposed between the top plate and the bottom plate so as to continue into the bottom plate; a feed core and a winding core having an ink ribbon wound thereon and placed in the cassette body; a ribbon outlet port formed on the wall plate for allowing the ink ribbon placed in the cassette body to be drawn out therethrough; the ink ribbon drawn out once from the cassette body through the ribbon outlet port being able to be drawn into the cassette body again and wound on the winding core; a pair of paper guide members disposed in the vicinity of widthwise ends of the ink ribbon drawn through the ribbon outlet port respectively so as to project from the wall plate of the cassette body in the direction in which the ink ribbon is drawn; and at least one of the paper guide members being formed with an inclined surface inclining in such a manner that the projecting length decreases from the projecting top toward the lateral center of the wall plate.
As a second measure, a ribbon guide member extending in one direction from the top plate of the cassette body is provided, and the ink ribbon may be wound in a state of being turned back at the ribbon turning-back portion provided at the distal end of the ribbon guide member.
As a third measure, the wall plate is formed continuously and integrally with an end of the bottom plate and with a connecting portion connecting the top plate and the ribbon guide member respectively, and is inclined gradually toward the ribbon turning-back portion as it extends from one end of the bottom plate toward the top plate.
As a fourth measure, the paper guide members are disposed at the equal distance respectively from the lateral center of the wall plate extending in parallel with the width of the ink ribbon with the inclined surfaces opposing with each other, and is formed into a tapered shape or a curved shape being symmetrical with respect to the center.